As I'm also a member on a mobile development forum (mainly surrounding Windows Phone and Android devices) and I've made around 13,000 posts in just over a year, I've clearly been around enough of that forum to see the difference between successful and unsuccessful threads and a myriad of reasons as to what makes them so.

From encountering so many threads over there, the following reasons are what I believe to be the most important factors in deciding a threads success;

*Responsiveness - This, in my opinion, is one of the most important reasons I'm listing. In a lot of cases, the OP will make a guide or start a discussion and it will be interesting and therefore start well. For whatever reason, the OP will stop posting in their thread. This could either be because they've forgotten about the thread, they've lost interest in the thread or a multitude of other reasons. Sometimes threads will still survive regardless of whether the OP is active in the thread or not. Most times, however, this is not the case and the thread will simply fall because the OP wasn't being responsive enough in the thread.

*Interest - Of course, the topic has to be interesting to people otherwise they won't want to post there. If I see yet another thread created which is simply discussing something which has been done multiple times before, I won't want to post there as it's boring.
Having said that, a thread can't only be interesting. It also needs to have good angles which can be discussed so that it can bring more participation to the topic.

*Layout - No matter how informative or interesting the thread may be, if the OP is looking messy/disorganised or they really haven't bothered to put the effort into the thread then I won't even bother reading it. After all, if the information was important that the layout would represent that and therefore be appealing purely from a first glance.

*Language/grammar - No-one wants to read a post which requires translating even though it's posted in "English". Things like "ermahgerd, diz thred is gr8 n I wnt to join" are bloody horrible to have to read and therefore people won't read it.
If all grammar is missing from the post and it's effectively 1 huge sentence with no breaks, people won't want to read it.
It's different, however, if English isn't the persons first language and you can tell they translated it to English so they could post it. In that instance, it's perfectly acceptable because if someone can't natively write in English, how can we expect them to get all spelling and grammar perfect when people who do write English can mess things up pretty badly.

*Posts/Views - Even though these stats can generally inform you as to whether a thread is doing well or not, I class this as the least important point out of all I've mentioned. Views won't necessarily mean a lot as people could simply open the thread purely based on an intriguing title. Posts don't always count for a lot either as we're all aware that a thread could have 3,000 posts yet only have 100 or less decent responses. The rest could be filled with arguments and people just posting crap.
What I'll generally do if I'm scouting out a popular and successful thread to get involved with, is I'll skip to random pages throughout the thread and look at the replies. If they're of good quality, I know that there's a good chance I'll enjoy posting in that thread and I will be able to join in with the different discussions taking place.

That's how I judge a successful thread anyway

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It's a good job that I'm not able to make my own ROM hack. It would be insanely difficult to complete, even for me!